Mutation for Creating Links

Setting up mutations is as easy as queries, following a very similar process.

All GraphQL mutations start from a root type called Mutation.

This type is auto generated in the file app/graphql/types/mutation_type.rb:

module Types
  class MutationType < BaseObject
    # TODO: remove me
    field :test_field, String, null: false,
      description: "An example field added by the generator"
    def test_field
      "Hello World"

This type is a placeholder for all GraphQL mutations.

To prevent any error when you first start your GraphQL project, it is generated with a dummy testField field. You will be able to remove it as soon as you add your own mutation below.

The mutation type is automatically exposed in your schema:

class GraphqlTutorialSchema < GraphQL::Schema
  mutation Types::MutationType
  query Types::QueryType

Resolvers with Arguments

Now add a resolver for createLink.

For this purpose, you’ll use a Mutation class, as mentioned earlier.

Testing with Playground

To test, just restart the server again and use the new mutation with GraphiQL:

Testing with Playground

Testing with Unit Test

It’s a good practice in Ruby to unit test your resolver objects.

Here is an example of Resolvers::CreateLink test:

require 'test_helper'

class Mutations::CreateLinkTest < ActiveSupport::TestCase
  def perform(user: nil, **args) nil, field: nil, context: {}).resolve(**args)

  test 'create a new link' do
    link = perform(
      url: '',
      description: 'description',

    assert link.persisted?
    assert_equal link.description, 'description'
    assert_equal link.url, ''

You can run the tests with the following command:

bundle exec rails test

Next Chapter


Learn best practices for implementing email-password authentication on a GraphQL Server written in Ruby.

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